Abnormal elastin fibers (fragmented, clumped) with variable changes in elastin contents could lead to emphysematous lungs.32–34 Two collagenases metalloproteinases, MMP2 and MMP8, and a cathepsin (CTSS) were identified to be upregulated in the COVID-19 lung tissue (Fig. 4e). Here, CTSS is linked to COVID-19.